Musical productions that sound agreeable but lack the form of an independent work of art are often used as background music in films, plays and other presentations. The quantitative need of this kind of music may be considerable. Quiet music is also used extensively in shops and other public premises to entertain customers and to create a desired atmosphere. One way of producing such background music is to use an electric device generating so-called synthesized music. Such devices comprise one or more electronic musical instruments or synthesizers and an automatic device producing control signals for them.
One way of producing such control code sequences and signals is to use so-called artificial intelligence programs utilizing heuristically rules based on musical expertise. The present invention, however, is not concerned with this kind of expert methods but with a device forming the required rules automatically on the basis of example material and producing new code sequences automatically with the aid of these rules. One such approach is disclosed in U.S. Pat. No. 4,926,737 to Minamitaka.
One prior art device producing control signals is based on Markov processes, in which each note (pitch, duration) is treated as a single stochastic state in a sequence of states. If example material, that is, note material, is given, the probability Pr of a state S.sub.i in the sequence is Pr(S.sub.i .vertline.S.sub.i-1, S.sub.i-2, . . . ) when the preceding states in the sequence are S.sub.i-1, S.sub.i-2, etc. Three preceding states are often sufficient to achieve a satisfactory outcome in music based on Markov processes. New music is generated by probability functions stored in the memory, starting from a key sequence to which is added a successor state having the highest probability on the basis of the probability function Pr and, e.g. the last three notes or states in the sequence. The sequence so increased is used as a new key sequence so that the process generates endlessly note code material and control signals for electronic musical instruments or synthesizers. Moreover, additional operations or rules are needed to produce typical musical structures from melody parts.
This prior art method of generating note codes requires large amounts of training material to form conditional probability density functions. In addition, synthesized music produced as described above does not usually comprise any surprise element and is monotonous, since each note has the same value in a stochastic process, whereas the same is not true with the properties of natural music.